Inert gas injection to help control or extinguish coal fires

Abstract

A method of locating and controlling subsurface coal fires is provided that includes mapping a subsurface coal bed fire using a magnetometer, where the mapping includes locating a combustion zone and an air inlet to the combustion zone of the coal bed fire, drilling an injection port from the earth surface to a previously burned zone of the combustion zone, where the injection port is disposed between the air inlet and the combustion zone, inserting a tube in the injection port, where the tube has an exterior tube seal disposed around the tube, and the exterior tube seal isolates the earth surface from the combustion zone along an exterior of the tube. The method further includes injecting an inert gas through the tube to the combustion zone, where the inert gas controls the combustion zone of the coal bed fire.

What is claimed: 
     
       1. A method locating and controlling subsurface coal fires, comprising:
 a. mapping a subsurface coal bed fire using a magnetometer, wherein said mapping comprises locating a combustion zone of said coal bed fire and an air inlet to said combustion zone; 
 b. drilling an injection port from the earth surface to a previously burned zone of said combustion zone, wherein said injection port is disposed between said air inlet and said combustion zone; 
 c. inserting a tube in said injection port, wherein said tube comprises an exterior tube seal disposed around said tube, wherein said exterior tube seal isolates said earth surface from said combustion zone along an exterior of said tube; and 
 d. injecting an inert gas through said tube to said combustion zone, wherein said inert gas controls said combustion zone of said coal bed fire by excluding air from said combustion zone. 
 
     
     
       2. The method according to  claim 1 , wherein said mapping is used for site selection, wherein said site selection comprises using magnetometer results, gas composition results, fissure mapping results, temperature results, or log results from drilling to determine a location for said injection ports with respect to said combustion zone of said coal bed fire. 
     
     
       3. The method according to  claim 2 , wherein said gas composition results are used to distinguish between burning regions in said coal bed fire and air saturated regions in said coal bed fire. 
     
     
       4. The method according to  claim 2 , wherein said temperature results are used to differentiate between the burned and unburned regions, wherein temperatures results that are above ambient temperatures denote some combustion activity. 
     
     
       5. The method according to  claim 2 , wherein said fissure mapping results are differentiated based on thermal signatures and physical characteristics, wherein said physical characteristics comprise fissure aperture, fissure length, fissure type, and fissure orientation. 
     
     
       6. The method according to  claim 2 , wherein said log results are used to confirm said magnetometer results, wherein said log results comprise well logs and drillers' logs. 
     
     
       7. The method according to  claim 2 , wherein said log results are used to determine locations of said injection ports, wherein at least two said log results are used to differentiate between burned and unburned regions in said coal bed fire. 
     
     
       8. The method according to  claim 1 , wherein said mapping comprises using a cesium-vapor magnetometer to delineate boundaries of current and previous burn regions in said coal bed fire. 
     
     
       9. The method according to  claim 1 , wherein said mapping comprises using a magnetometer to distinguish areas of relatively high, relatively low, and relatively neutral magnetic anomaly regions when compared to the earth's magnetic field strength. 
     
     
       10. The method according to  claim 9 , wherein said relatively high magnetic anomaly regions outline areas where said coal bed fire has previously burned, wherein said relatively low magnetic anomaly regions outline areas where said coal bed fire is currently burning, and wherein said relatively neutral magnetic anomaly regions outline unburned coal seams. 
     
     
       11. The method according to  claim 1 , wherein said mapping comprises drilling boreholes below currently burning, previously burned, or unburned regions in said coal bed fire, wherein gas samples are collected there from. 
     
     
       12. The method according to  claim 1 , wherein said mapping comprises using subsurface thermocouples disposed in said coal bed fire, or disposed above said coal bed fire for measuring the temperatures in subsurface regions. 
     
     
       13. The method according to  claim 1 , wherein bentonite chips are disposed to fill the region above said isolator seal up to said Earth's surface, wherein said bentonite chips seal off any flow paths up along said injection port to said Earth's surface. 
     
     
       14. The method according to  claim 1 , wherein injecting said inert gas comprises identifying and characterizing a dominant exhaust fissure exhausting gas from said coal fire bed, wherein said characterizing comprises estimating a flux of said exhaust gas using assumptions about length of said dominant exhaust fissure and surface roughness coefficients of said dominant exhaust fissure. 
     
     
       15. The method according to  claim 14 , wherein said characterization is corroborated using a volatile organic compound digital camera (VOC camera) to measure a rate of an exhaust plume exiting said dominant exhaust fissure, wherein a plume velocity, and dominant exhaust fissure dimensions, are used to estimate said exhaust gas flux, wherein a rate of said inert gas supplied through said injection port is determined. 
     
     
       16. The method according to  claim 1 , wherein stable isotope measurements are made at an exhaust fissure from said coal fire, wherein said isotope measurements are used to determine a present of said injected inert gas. 
     
     
       17. The method according to  claim 1 , wherein said injected inert gas is selected from the group consisting of He, Ne, Ar, Kr, Xe, Rn, SF 6 , N 2  and CO 2 .